Even though thermoelectric effects have drawn more attention these days due to environmental and economic reasons, the efficiency of the thermoelectric technology is still limited by currently available thermoelectric materials. The priority aim in thermoelectric industry is to achieve a higher ZT, the dimensionless thermoelectric figure of merit. There are key thermoelectric properties determining the efficiency ZT: Seebeck coefficient, electrical conductivity, and thermal conductivity. This work mainly focuses on strategies to obtain higher ZT and will walk through each thermoelectric property calculation for bulk and nano-scaled semiconductors using Landauer and phonon Boltzmann transport approaches. As a reduction of thermal conductivity in nanoscale semiconductor wires has been reported for the last decade, scaling of semiconductor devices changes the way heat flows through a system due to a significant increase in boundary scattering. It will be well shown that the thermal conductivity of nanoscale semiconductors significantly decreases compared to that of bulk semiconductors. Considering an enhancement of ZT, a decrease in thermal conductivity is a significant issue in designing new devices while retaining electrical conductivity. Therefore, at the end, geometrically engineered semiconductor nanowires and superlattice nanowires will be investigated to show even more reduced phononic transport properties compared to the straight and pure semiconductor nanowires. These results will be expected to suggest prospective ideas to improve the current thermoelectric technology.